Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to an apparatus and method for tomosynthesis imaging. The apparatus and method of the invention is capable of increasing patient throughput, increasing patient comfort, and decreasing radiation dose through the use of a single wide-angle tomosynthesis scan.
A widely used imaging tool for the early detection of breast cancer is x-ray mammography. In conventional x-ray mammographic imaging, a breast is immobilized and imaged in two different positions, thereby acquiring two separate projection images (views). The two views are known as cranio-caudal (CC) and mediolateral oblique (MLO) projections. A CC projection is taken from above the patient, while an MLO projection is taken from an oblique side angle. FIGS. 1 and 2 illustrate a conventional CC projection 100 and MLO projection 200, respectively. As FIG. 1 shows, a patient's breast 102 is immobilized and compressed between a compression paddle 104 and a platform 106, shown in a horizontal orientation (i.e., generally perpendicular to the long patient axis). Below platform 106 is a detector 108, which receives x-ray beams emitted from an x-ray source 110. Similarly, the MLO projection 200 illustrated in FIG. 2 shows that a patient's breast 102 is immobilized and compressed between a compression paddle 104 and a platform 106, albeit at an angle different than that of the CC projection 100 with respect to the long patient axis. Again, a detector 108 is located below platform 106 with respect to the projection direction to receive x-ray beams emitted from an x-ray source 110.
Mammographic images based on the CC and MLO projection views are interpreted by trained clinicians to detect and identify potentially cancerous lesions in breast or other tissue. Unfortunately, images based on conventional projection views lack sensitivity and can be difficult to read due to the fact that superimposed tissue may mimic a lesion, or a lesion may be hidden by superimposed structure. Acquiring both a CC view and an MLO view partially addresses this issue, and thus the likelihood of detecting a lesion (or lesions) is increased. However, one still observes a high rate of false negative and/or false positive results. Furthermore, each of the CC and MLO projection views require separate breast compressions, leading to increased radiation dose, increased patient discomfort and reduced patient throughput.
In an effort to address the inadequacies of conventional mammographic imaging using separate CC and MLO projection views, a mammographic technique known as three-dimensional tomosynthesis imaging was developed. Tomosynthesis imaging was found to help in resolving the ambiguities associated with overlapping tissue mimicking a lesion or overlying tissue hiding a lesion, two major causes of false positives and false negatives in conventional mammographic imaging techniques. As FIG. 3 illustrates, a three-dimensional tomosynthesis scan 300 involves the movement of an x-ray source 310 in an arced or linear path at a predefined angle about a patient's breast 302, with patient's breast 302 again immobilized and compressed between a compression paddle 304 and a platform 306. A detector 308 is located below platform 306, where detector 308 receives x-ray beams emitted from x-ray source 310. Typical three-dimensional tomosynthesis imaging uses a stationary flat-panel x-ray detector and acquires a set of projection images (i.e., the tomosynthesis image dataset) in a step-and-shoot mode (i.e., the x-ray source moves between exposures, and a new exposure is taken at each new x-ray source position along the path). Projection angles of the x-ray source 310, which correspond to the positions of x-ray source 310 at which projection images are acquired, are arranged in a 1D or 2D path, which is generally symmetrical around the z-axis, i.e., the axis orthogonal to the x-ray detector plane. From the tomosynthesis image dataset a volumetric 3D dataset is reconstructed in a coordinate system where the x/y plane corresponds to the detector plane, and the z-axis is the axis orthogonal to the detector plane. The reconstructed volume is generally arranged as a set of x/y slices 312 for different z-values (or heights above the detector), wherein the slices are arranged parallel to the x-ray detector plane.
Viewing of the reconstructed volume in conventional tomosynthesis is generally performed in a slice-by-slice mode (e.g., in a cine-loop). Other viewing modes (e.g., thick slices, volume rendering, etc.) are used as well. It is important to note that slice-by-slice viewing of the 3D volume reconstructed in the x/y/z coordinate system implies a view direction 314 of the reconstructed volume in the z-axis direction. Also, the reconstruction algorithms in conventional tomosynthesis imaging are implicitly optimized for the conventional viewing techniques, and thereby discard some image information that is present in the tomosynthesis image dataset, which degrades the perceived image quality for the implicitly chosen viewing direction. Using novel approaches, such as those discussed herein, the image information from the tomosynthesis image dataset may be fully used.
While three-dimensional tomosynthesis allows significant improvements in detection and recall rate, a single tomosynthesis acquisition sequence at a small acquisition angle (e.g., ±15 degrees), such as that shown in FIG. 3, is insufficient for ideal three-dimensional imaging. Thus, conventional tomosynthesis imaging techniques incorporate a second tomosynthesis acquisition sequence, such as tomosynthesis scan 400 shown in FIG. 4, into the imaging procedure. By acquiring images using tomosynthesis imaging from two views (i.e., those shown in FIGS. 3 and 4, corresponding to the conventional CC and MLO views), benefits similar to those found in conventional mammographic imaging using separate CC and MLO projection views can be achieved, while each individual tomosynthesis dataset exhibits better clinical performance than its single-image counterpart. However, the relatively small angular range scan in each of the two tomosynthesis acquisitions is not sufficient to produce an image dataset having good three-dimensional resolution. Additionally, by acquiring images via two acquisitions, two separate breast compressions are again needed, thereby adding to patient discomfort, radiation dosage, and scan time. The breast compressions also limit the benefits of three-dimensional tomosynthesis imaging, as the breast is essentially compressed into a flat configuration.
Therefore, it would be desirable to design an apparatus and method of wide angle, multi-view mammographic tomosynthesis imaging without the need for breast repositioning or multiple breast compressions, which fully utilizes the collected information contained in the tomosynthesis image dataset.